Several known methods are based on determining the time it takes to consume a given amount of fuel; that is, the time is recorded at start and stop of the consumption of the predetermined amount of fuel without any monitoring of the process during the fuel consumption.
Austrian Patent 298 821 relates to a measuring device for measuring the fuel consumption of an internal combustion engine on a test bench. It consists of two measuring pots, each one supported by a weight measuring device based on the strain gauge principle. The pots are connected to a common fuel tank, and each one of the pots is connected to the internal combustion engine. The lines between the fuel tank and the measuring pots, as well as the lines between the measuring pots and the internal combustion engine, are equipped with electrically controlled valves. The measuring pots are drained and filled alternately by a switching device that opens and closes the valves in response to pulses from the weight measuring devices. As soon as preset maximum and minimum values of the weight of the pots are registered by the measuring devices, they transmit pulses to the switching device. The measuring period is divided into a number of time intervals, during which a fuel consumption corresponding to the change in weight of the measuring pots is determined.
The total fuel consumption during the measuring period is determined by adding the consumption of the time intervals together.
This method has the disadvantage that if disturbances occur during the measuring period, in the form of changes in engine speed or torque, and this is not detected, an erroneous result can be obtained. Also, even small measuring errors at start and stop will cause direct errors in the overall result.